2. Field of the Invention
The present invention relates to an ophthalmic measurement apparatus, and more particularly to an ophthalmic measurement apparatus which measures biological properties (for example, blood cells, cell parts detached from tissues, pigment cells, lipid, protein, floating cells, etc.) by spatially scanning the anterior chamber of an examinee's eye with a laser beam and receiving light scattered by biological particles in the anterior chamber and which can also determine the state of alignment of the apparatus with the eye.
2. Prior Art
A flare meter is conventionally known as an ophthalmic measurement apparatus which performs measurements after first determining the state of optical alignment by irradiating the anterior chamber of the eye and receiving light scattered and reflected therefrom.
A flare meter is used to measure the protein concentration (flare concentration) in the anterior chamber. Based on the assumption that the flare concentration in the anterior chamber is uniform, it is only necessary to measure the protein concentration at one point. To align the system prior to measurement, therefore, it is only necessary to know the state of alignment spatially in one dimension.
However, two-dimensional laser beam sweeping is required to measure indicators of biological properties formed by physical quantities having a spatial distribution, such as the density of floating particles in the anterior chamber or the protein concentration. It therefore follows that it is also necessary to sweep the laser beam two-dimensionally for alignment purposes.
Conventional ophthalmic measurement apparatuses are aligned in such a way that they work as a means for obtaining one-dimensional alignment information and an alignment determination function for selecting the optimum position for measurement.
As an example, a method of alignment used for a non-contact tonometer provides the optimum position for correctly measuring the intraocular pressure by bringing the corneal axis connecting the center of corneal curvature with the corneal apex into alignment with the optical axis of the optical observation system, and adjusting the distance between the center of corneal curvature and the tip of the nozzle.
On the other hand, alignment with a refractometer obtains the optimum position for measuring refractivity by using two reference beams to form an image at one point on the retina.
However, the above types of alignment arrangements are not suitable for use in locating an optimum place to measure physical quantities indicative of biological properties having a spatial distribution such as the density of floating particles in the anterior chamber or the protein concentration, thus resulting in a reduction of the 5 measurable range (what is determined as being measurable). The fact that the measurable range is thus severely restricted means that the alignment takes much time. Moreover, the condition of the patient's eye may further restrict good alignment locations, so that even more time is required for alignment. The result is that more time is needed for measurement, subjecting both the examiner and the examinee to physical and mental stress and discomfort.
An object of the present invention is to provide an ophthalmological apparatus being capable of determining system alignment to expand the measurable region, reduce measurement time and improve measurement accuracy in measuring biological properties by spatially scanning the anterior chamber of an examinee's eye with a laser beam and receiving light scattered by biological particles in the anterior chamber.